In W-CDMA (Wideband Code Division Multiple Access), which is the third-generation mobile communication system, a user equipment (UE) in a CELL_FACH (Forward Access Channel) state does not specify a base station to which it belongs but selects a base station to which it belongs each time it transmits control information or the like. An operation of a RACH (Random Access Channel), which is an uplink data channel, is defined in the specification of the third-generation mobile communication system standardization project 3GPP (3rd Generation Partnership Project) (cf. e.g. Non Patent Documents 1 to 4). Further, in 3GPP Release 8, an E-RACH (Enhanced RACH) is being studied as an enhanced technique of the RACH (cf. e.g. Non Patent Document 5). An operation of the E-RACH is briefly described hereinafter with reference to FIGS. 1 to 3.
FIG. 1 is a block diagram showing a configuration of a mobile communication system. In order to avoid complicated description, it is assumed that a plurality of user equipments 20-1, 20-2, 20-3 and 20-N are located within a cell of a base station 10, and the user equipments are in the CELL_FACH state. It is also assumed that the base station 10 is connected to a host network device 30. Note that a given user equipment is referred to as “user equipment 20”.
FIG. 2 is a diagram showing an operation of the E-RACH, and FIG. 3 is a sequence chart of channel setting such as the E-RACH. Referring to FIG. 2, uplink communication involves an uplink data channel E-DCH (Enhanced Dedicated Channel) and a preamble part for providing timing before transmitting the E-DCH. Downlink communication involves a downlink channel AICH (Acquisition Indicator Channel) for responding to the preamble part received from the user equipment.
In the preamble part, a preamble signature Csig,s and a spread code called a preamble scrambling code Sr-pre,n, which are described later, are used. The preamble signature Csig,s consists of 4096 chips, which is a sequence of 256 repetitions of Hadamard codes with a code length of 16, and the preamble scrambling code Sr-pre,n is a cell identification code that is notified from the base station. The preamble signature Csig,s is randomly selected from predetermined preamble signatures (Csig,1, Csig,2, . . . Csig,s) by each user equipment.
Code data Cpre,n,s of the preamble part consists of the corresponding k-th preamble signature Csig,s among the 4096 chips and the preamble scrambling code Sr-pre,n as represented by the following mathematical expression (1).
                    [                  Expression          ⁢                                          ⁢          1                ]                                                                                  C                          pre              ,              n              ,              s                                ⁡                      (            k            )                          =                                            S                                                r                  -                  pre                                ,                n                                      ⁡                          (              k              )                                ×                                    C                              sig                ,                s                                      ⁡                          (              k              )                                ×                      e                          j              ⁡                              (                                                      π                    4                                    +                                                            π                      2                                        ⁢                    k                                                  )                                                                        (        1        )            k=0, 1, 2, 3, . . . , 4095Cpre,n,s: Preamble part code dataSr-pre,n: Preamble scrambling codeCsig,s: Preamble signature
The uplink data channel E-DCH is constructed on the basis of the specification defined in 3GPP Release 6 (cf. e.g. Non Patent Document 6).
As shown in FIGS. 2 and 3, the user equipment 20 first transmits preamble part code data with an initial transmission power value that is calculated from a reception electric power of a pilot channel of the base station 10 to the base station. The preamble part code data is generated by using the preamble scrambling code that is notified from the base station 10 and the preamble signature that is randomly selected by its own equipment as described above. For the received preamble, the base station 10 transmits a reception result (ACK/NACK/NoACK) to the user equipment 20 by using a plurality of AICH signature states. The AICH signature state is a code corresponding to the contents of notification. The base station 10 transmits a response to the preamble signature that is transmitted from the user equipment 20 to the user equipment at the same time. For the ACK response, an E-DCH transmission profile information number indicating E-DCH transmission profile information, which is described later, is also transmitted to the user equipment at the same time.
For example, a reception result “ACK” is notified when allowing transmission of uplink data with use of the E-DCH for the user equipment that has selected the preamble signature that is used in the preamble which is successfully received by the base station 10, and “NACK” is notified when not allowing it. Further, for the preamble signature that is not used in the preamble which is successfully received, “NoACK” is set as a response in the AICH.
The user equipment 20 receives the reception result through the AICH, and if a response to the preamble signature that is used in preamble transmission is ACK, it determines E-DCH transmission profile information by the below-described method and transmits data to the base station 10. If a response to the preamble signature that is used in preamble transmission is NACK, it performs preamble transmission again after a predetermined period of time. If a response to the preamble signature that is used in preamble transmission is NoACK, the user equipment 20 determines that the base station 10 does not receive the previously transmitted preamble and, if the number of times of retransmission does not reach the upper limit, it increases the transmission power of the preamble by a predetermined amount and carries out retransmission. Note that a minimum retransmission interval τp-p,min of the preamble part and an interval τp-a between the preamble part and the transmission of a reception result in the AICH are respectively determined in advance as shown in FIG. 2. The AICH transmits a reception result (ACK/NACK/NoACK) using a plurality of AICH signature states so as to correspond to the preamble signature Csig,s of the preamble.
The AICH is constructed by combining 32 codes aj derived from the following mathematical expression (2), and signature patterns bs,j of the AICH are defined in the table 1 (cf. e.g. Non Patent Document 4). Here, s indicates a signature number, and bs,j can be 16 patterns. Further, AIs indicates a signature state, and it is transmitted in the AICH as AIs=+1 when a preamble reception result is ACK, AIs=−1 when it is NACK, and AIs=0 when it is NoACK.
                    [                  Expression          ⁢                                          ⁢          2                ]                                                                      a          j                =                              ∑                          s              =              0                        15                    ⁢                                          ⁢                                    AI              s                        ⁢                          b                              s                ,                j                                                                        (        2        )            
TABLE 1sbs, 0, bs, 1 . . . , bs, 310111111111111111111−1−111−1−111−1−111−121111−1−1−1−11111−1−1−1311−1−1−1−11111−1−1−1−11411111111−1−1−1−1−1−1−1511−1−111−1−1−1−111−1−1161111−1−1−1−1−1−1−1−1111711−1−1−1−111−1−11111−18111111111111111911−1−111−1−111−1−111−1101111−1−1−1−11111−1−1−11111−1−1−1−11111−1−1−1−111211111111−1−1−1−1−1−1−11311−1−111−1−1−1−111−1−11141111−1−1−1−1−1−1−1−11111511−1−1−1−111−1−11111−1sbs, 0, bs, 1 . . . , bs, 310111111111111111111−111−1−111−1−111−1−111−1−12−11111−1−1−1−11111−1−1−1−13111−1−1−1−11111−1−1−1−1114−111111111−1−1−1−1−1−1−1−15111−1−111−1−1−1−111−1−111611111−1−1−1−1−1−1−1−111117−111−1−1−1−111−1−11111−1−181−1−1−1−1−1−1−1−1−1−1−1−1−1−1−1−19−1−1−111−1−111−1−111−1−11110−1−1−1−1−11111−1−1−1−11111111−1−11111−1−1−1−11111−1−112−1−1−1−1−1−1−1−1−111111111131−1−111−1−11111−1−111−1−1141−1−1−1−111111111−1−1−1−115−1−1−11111−1−111−1−1−1−111
The E-DCH transmission profile information is made up of UL (Uplink) scrambling code, E-RNTI (Enhanced Radio Network Temporary Identity), DPCCH (Dedicated Physical Control Channel) code and timing offset, E-RGCH (E-DCH Relative Grant Channel) code, E-HICH (E-DCH Hybrid ARQ Indicator Channel) code, E-AGCH (E-DCH Absolute Grant Channel) code or the like. The base station sends an E-DCH transmission profile information list that includes a plurality of pieces of E-DCH transmission profile information and E-DCH transmission profile information numbers corresponding to the respective pieces of E-DCH transmission profile information to a user equipment in the cell on a regular basis through a BCH (Broadcast Channel). Then, the user equipment transmits a preamble. The base station transmits a reception result ACK by using the AICH and, at the same time, selects one E-DCH transmission profile information number and allocates it to the user equipment. The user equipment decides a transmission profile from E-DCH transmission profile information corresponding to the allocated E-DCH transmission profile information number and transmits uplink data to the base station (cf. e.g. Non Patent Document 7). A plurality of E-DCH transmission profile information numbers are allocated to one preamble signature. Further, the E-DCH transmission profile information number is specified by using an AICH signature combination. The AICH signature indicates a pair of an AICH signature number and an AICH signature state associated therewith, and a combination of a plurality of AICH signatures is called a signature combination. Further, a set of a plurality of AICH signature combinations is called an AICH signature combination set. The table 2 is an example of an AICH signature combination set table showing the AICH signature combination set.
TABLE 2E-DCH TRANS-MISSIONPROFILE AICH RE-INFOR-PREAMBLESIGNATURE CEPTIONMATIONSIGNATURECOMBINATIONRESULTNUMBER11, 2, 3 (0, 0, 0)NO ACK—11, 2, 3 (−1, −1, −1)NACK—11, 2, 3 (−1, −1, +1)ACK111, 2, 3 (−1, +1, −1)ACK211, 2, 3 (−1, +1, +1)ACK311, 2, 3 (+1, −1, −1)ACK411, 2, 3 (+1, −1, +1)ACK511, 2, 3 (+1, +1, −1)ACK611, 2, 3 (+1, +1, +1)ACK7
Referring to the case where the reception result is ACK and the E-DCH transmission profile information number is 1 in the table 2 as an example, the AICH signature combination that is made up of three AICH signatures with the signature number of “1, 2, 3” and the signature state of (−1, −1, +1) is shown.
[Non Patent Document 1]
    3GPP TS25.214 v7.5.0 May 2007[Non Patent Document 2]    3GPP TS25.321 v7.2.0 September 2006[Non Patent Document 3]    3GPP TS25.331 v7.3.0 December 2006[Non Patent Document 4]    3GPP TS25.211 v7.3.0 September 2007[Non Patent Document 5]    3GPP RP-070677 Nokia Siemens Networks, Nokia, Ericsson, Qual comm, T-Mobile, Telecom Italia, “Enhanced Uplink for CELL_FACH State in FDD” September 2007[Non Patent Document 6]    3GPP TS25.319 v7.3.0[Non Patent Document 7]    3GPP R2-074626 Nokia Corporation, Nokia Siemens Networks, “Resource assignment for E-DCH access in CELL_FACH state” November 2007